1. Field of the Invention
This disclosure relates to a method of sensing touch, and more particularly, to an optical touch input system configured to detect correct touch without reference to errors caused by positional variation and misalignment of optical sensor modules located in at least three corners of a display panel. Retro-reflectors are configured to retro-reflect light emitted by the optical sensor modules.
2. Discussion of the Related Art
In general, a touch input system is one of the components that interface between telecommunication devices having a variety of display types. A user may touch a screen of the touch input system by using a pen or finger.
The touch input system is an input device used by a wide variety of people because of its convenience and ease of use. As a result, the touch input systems are used in many applications, for example, certificate-issuing devices used in banks or public offices, various medical apparatus, guide devices used in sightseeing, guide devices for traffic systems, and the like.
The touch input system may be categorized into a resistive type touch input system, a micro capacitive touch glass, an ultrasonic wave glass, and an infrared type touch input system, based on a touch recognition type.
The resistive type touch input system is made of two transparent conductive layers. A bottom layer is formed of glass having a conductive material coated thereon, and a top layer is formed of film having conductive material coated thereon. The two layers are spaced apart by a predetermined distance by a micro-printed spacers, which electrically insulate the two layers. A predetermined voltage is applied to the two layers, respectively. When a finger, touch pen, or other object touches the top layer, a resistance of the top layer (X axis) or the bottom layer (Y axis) changes according to the location of the touch. Predetermined X and Y locations corresponding to the changed resistive values are computed by a controller, and the controller displays coordinates on a monitor or data is inputted and used as coordinate data.
The micro capacitive touch glass is made of a transparent glass sensor having a thin conductor coated thereon. An electrode pattern is precisely printed along an edge of a conductor layer, and a transparent glass protection coating layer is in close contact with the conductor layer to protect and cover the sensor. A voltage is applied to a screen, and the electrode pattern forms a low voltage field on a touch sensor conductive surface. When an object or finger touches the screen, minute currents are generated at touch points. The distance of the current flow from each corner is proportional to the distance from the corner to the object, such as the human finger. Accordingly, the touch screen controller computes the ratio of the current flow to detect the touch point coordinates.
The ultrasonic wave touch glass is made of 100% glass, and is not affected by surface damage or abrasion, compared with the other types of screen surfaces, where damage or abrasion would reduce the usage life of such a touch screen. A touch screen controller transmits an electric signal of 5 MHz to a transmitting converter configured to generate ultrasonic waves. The reflected waves pass over the panel surface. When a user pushes the touch screen surface, part of the ultrasonic waves passing the touch point is absorbed by the user. A received signal and a lost or reduced signal in a digital map may be identified by a controller, and a coordinate value of the point corresponding to the current change of the signal may be calculated accordingly. This process may be independently implemented with respect to the X and Y axes.
The infrared type touch input system uses an inherent property of an infrared ray in that a line-of-sight path is required. The infrared ray is blocked when it encounters an obstacle. A portion of the touch input system having pressure applied thereto by an object blocks the infrared rays emitted along horizontal and vertical directions. The X and Y coordinates of the blocked points are sensed. The infrared type touch input system identifies the touch point from the blockage of infrared scanning beams. To form a invisible infrared matrix, an infrared ray beam is emitted from a predetermined surface of each of X and Y axis, and the emitted infrared ray is received by the sensors on opposite sides of the touch input system.
Each touch input system has different advantages, and the infrared type touch input system has been receiving attention because of its convenience of installation and because it requires a very small pressure for activation and sensing.
An infrared type touch input system of related art will be described in reference to FIG. 1 as follows.
FIG. 1 is a plan view illustrating an infrared type touch input system of the related art.
As shown in FIG. 1, the infrared type touch input system includes a panel 10, infrared sensors 5 (and emitters) provided at two adjacent corners of the panel 10, and a reflector 7 provided in each of three sides of the panel 10.
In the related art panel, light emitted from the infrared sensors 5 (emitters) located in both opposite ends of the panel 10 is reflected, and the emitted light is blocked by the touch of the object, such as a finger. An angle formed by the light received may be computed to determine the location of the touch.
When the infrared type panel of the related art uses only two cameras, touch resolution is low in an upper area because a dead zone is generated, as shown in FIG. 1. Each point shown in FIG. 1 is the lowest resolution measurable by using triangulation.
Such a dead zone is generated in a predetermined area in which an angle formed by the infrared sensors 5 is greater than predetermined value, and touch detection cannot be implemented in the dead zone. Thus, touch sensing accuracy may deteriorate in this predetermined area, and thus it is necessary to compensate for the reduced accuracy. To compensate, the infrared sensors are positioned on the far outer corners of the touch panel so as to position the dead zone outside the viewing perimeter of the liquid crystal panel. Therefore, the touch input system is required to have a size greater than the size of the liquid crystal panel. As a result, a non-effective area exists and the touch input system must be larger than is otherwise required.
Typically, the touch input system and the liquid crystal panel are separate components. In manufacturing, complex methods are required to combine elements of each panel with each other and to couple the touch input system to a liquid crystal module.
Furthermore, it is difficult to select accurate coordinates in such a touch input system of the related art, and there is a disadvantage that only one touch point at one time can be recognized. In other words, when two points are simultaneously touched on the touch input system, the touch input system fails to recognize the touch or it recognizes only the first of the two touches, which may cause an error.
Two infrared sensors and reflectors may be used to determine touch coordinates by using triangulation. Typically, two light sources and sensors are located in an upper area of the touch input system, and the reflectors are located in three surfaces to retro-reflect the light emitted from the light sources. The light is blocked when the panel is touched with an object, which is sensed by a controller, and a corresponding angle of the received light is computed to recognize the touch. Tolerance or variation in the physical orientation of the infrared sensors (misalignment) may occur during manufacture and assembly of the infrared type touch input system of the related art, and such misalignment may cause touch errors.